Ultrafast switching dynamics in short pulse laser-driven phase change materials

• Applicant: Professor Dr. Klaus Sokolowski-Tinten
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2012 to 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 224652279

Ultrafast time-resolved X-ray scattering will be used to study the structural dynamics in chalcogenide-based phase change materials (PCMs) after short pulse laser irradiation. In particular, we would like to identify thermal and possibly non-thermal transition pathways between their amorphous and crystalline phases, investigate how the structural dynamics depend on laser parameters such as excitation strength and pulse duration, and clarify which processes determine and limit the ultimate switching speed. Thin films of the prototypical PCM Ge2Sb2Te5 (GST225) as well as other chalcogenide alloys will be irradiated by short (fs to ps) optical laser pulses. The structural changes during the laser-induced transitions from the crystalline to the amorphous state and vice versa will be monitored by scattering of a time-delayed hard X-ray probe pulse in normal-incidence transmission geometry. Taking full advantage of the high flux and the short pulse duration of the LCLS the planned measurements of the scattering pattern as a function of the pump-probe time delay provide the transient structure factor S(q) and thus information on the structural properties of PCMs during switching. The possibility to obtain high S/N scattering data with single LCLS-pulses allow dynamic structure measurements under "real life" switching conditions which have not been possible before or with any other existing X-ray source.

• DFG Programme: Research Grants